Peak detector circuits are generally an integral part of automatic gain control (AGC) loops. There are basically two types of peak detector circuits which are used in AGC loops. The first type is a fast charge and slow discharge peak detector and the second type is an averaging detector. The fast charge, slow discharge detector reacts quickly to a signal which is increasing in amplitude, but reacts slowly to a signal which is decreasing in amplitude. The averaging detector, on the other hand, reacts slowly to both increasing and decreasing amplitudes of an input signal.
In certain applications it is desired to have a peak detector which reacts quickly to both an increasing amplitude and a decreasing amplitude of the input signal. This is essentially a requirement that the peak detector rapidly follow the amplitude of the input signal. Conventional peak detectors work best with input signals which have equal energy in each bit. But when the input signal does not have equal energy in each bit, such as with phase shift keyed (PSK) signals, an averaging detector produces a noisy output signal.
Therefore, there exists a need for a peak detector which rapidly follows both increasing and decreasing amplitudes of an input signal and is not affected by an input signal which does not have equal energy distribution for each of the bits.